Cellulose lacquer composition



Patented Apr. 2, ,1935 v t 'The present invention relates to method for preventingthe yellowing of pigmented cellulose Cellulose lacquer films containing white pigments in the past have fbeen found to be poorly suited for some purposes due Q to the tendency shownjiby such films to-turn yellow when exposed toeither'diifused or'directsunlight. The

degree and speed of 'this' coloration of pigmented nitrocellulosev lacquer i films has been: j found to depend to a large degree upon cert'ai'n definite factors. For example, it has been foundthatfllms contaming wgums, zresins; pigments, etc. but 'no nitrocellulose; are generally notfsu'bject ,to: yel-' lowing; Likewise,lfilmscontaining nitrocellulose, V pigmentaetcubutno gums or resins, are genera ally not ,subjectito yellowing." On the other'hand, 1 films containing; both: nitrocellulose. and gumsior I resins; as well as .ipigments and -1 other; materials are subject to yellowingsin varying degrees deand gums or resinsemployedd l Of-thevario'us gumsor resins commonly used in the production of lacquers, ester gum appears to causejvthe most difficultyein'regards yellowing due both; to the degree of, yellowing and the expendentuponthe particular pigment or pigments tent of its use, altho whitezpigmentedqlacquerscontaining, a mixtureoi ester gum: and a phenol? formaldehyde ,resin, yellow more extensivelyeven than sir nilar, films 7 containing only ester fglll'fl". Fllmscontain ing such gums as kauri, elemi, mas tic, congo,*etc..- a lso turn yellow butnotrto the same degreeassimilarfirms containing thelmuch moreextensively usedester All whitepigment d trocellulose lacquerfilms containing gums or resins such as those justmentionedappear to be subject to the disadvantage of yellowing under certain conditions. This is particularly the case when such films are exposed to direct or diffused sunlight, under ordinary conditions of exposure, with thesingle exception of films of this character which contain zinc oxide as the white pigment. For some unexplained reason such films appear not to be subject to the degree of yellowing to which other white pigments such as titanium dioxide, mixtures of titanium oxide and barium sulphate, mixtures of zinc sulphide. and barium sulphate antimony oxide, zinc sulfide, white lead, etc. are subject under similar circumstances. elevated temperatures, such asare ordinarily attained in wall surfaces located close to radiators, even films containing zinc oxide asthe pigment are subject to very deoidedsyellowing. The samething is true evenatordinary temperaturesin the ewe;

cEtLuL-osn Lacounacomosrrro Charles. Bogin, Tel-re n me, I 1nd; 7 assign V communa Solvents"Corporation; Tei-reflaute,

51nd,, a corporation'of lt iaryland" .take place between-.acidsefrom'=thejresinsr0-n gum However, at somewhat,

case offilms' containing some other white pig ment"in addition to zinc*oxideif a Altho 1 it has been: rlotd that: the yellowing of lacquer films generallytakes/f place' only when nitrocellulosa g-ums for iresins'iand aiwhite' pig- 5 ment (other-thahlzinc oxide, except atrtemperatures above iroom temperature )1; are present together, it is .no'tdefinitely, known what; agency is responsible.-forrthisfiparticularseffect; @Varioustheories as to theicause of thisiphenomenon have 10 been: advanced, *the most-'--probable ofrzwhich lap pearsltorindicate' ethat tlie yellowing-:oi the filmiis brought, aboutas the result-pf reactions which and thenitrocelluloseand/ompigment 1 It hasanow, been discovered thatythe yellowing of; :white; pigmented nitrocellulose lacquers :con': taininggums or resins may be.effectively-reduced and'irr-most casese entirelysuppressed by the in;

corporation in the.-r.lac,quer;,-of awsm'allipamount offgo' an alkali such, as,-:-fo r; exampla calcium,barium, V I strontium,.magnesium, sodimn potassiurn oxide Tor; hydroxide. ;:'I he:i amount: of agent 1 required depends; naturallyz upon theiparticnlar pigment or pigments and resins or gums. jusedrin the, lacquenand tobsome extentgupon the particular alkali used,in:preventingryellowingor: the pig-s I vmentedsfilmpg Since mixtures: of ester gum and e phenolformaldehyde resins; and; even ester: gum

per sagenerallmbring about-3a greater degree of -36) yellowing than when: dammar: is

used; it is gen- I 7' any-"necessary u r i r poruons of alkali in?compositionsscontaining theselgurnsfthan is the; case; withusimilar compositions. containing Y dammar; Similarlyrsince 5ateordinaryjtempera 35 tures little--or. no; yellowing itakes; place in: films containing; zinc oxide as'rthe pigment, :the amount of :alkali I; which; {is-incorporatedin; such: 'compoe sitions may be greatly reduced, unless of course,

the lacquer is to be used where the film will be-uo subjected-to high temperatures, which as has previously been noted, causes distinct yellowing even inthe case of zinc oxide; 7 7 When appreciable amounts 'of zinc oxide are used together with other pigments'more susceptible to yellowing, the tendency for the film thereby obtainedto yellow is appreciablylessenedbut even in this case the addition of an'alkali has a marked efiect inreducing-thedegree of yellowingfurther. 1 The method of preventing the yellowin O pigmented lacquer'filmsherein disclosed is of :the

greatest commercial'imp'ortance in nitrocellulose lacquer films containing ester gum and titanium dioxide. due to the cheapnessiand general use 5 e 1 l itfiis of the former and; the high covering power and general desirability of the latter. "The use of small amounts of alkali veryaeffectively reduces theItendencyof such films to turn yellow.

The amount of alkali which it is-desirable or necessary to employ; as indicatedabove, depends and 1.0%" magnesium, oxide, 0.4% barium -1 1'y'-. droxide ande0.1% sodium hydroxide} ln asimi- 'lar lacquer containing'dammarin place ofester gum, 0.05% lime was foundto be .suffieientto. prevent yellowingof theres ulting film. "Thefyellowing .of 'zinc: oxide-estersgummitrocellulose lacquers at 60 C. islessene'dj; by .the -incorporae tion in the lacquer of 0.1%-lime.

a "I'he incorporation' of; small-amounts offalka lies white pigmented nitrocellulose. lacquers which tend to yellow; or :the treatment of the gums or resins to be' used. in .such'lacquers with .alkalie's, in general, materially lessens. anyitend-q ency possessed byzthe filmsproduced by suchlace quers to-turn yellow} In the "case of films con+ taining antimonyoxide, however, "this procedure apparentlylisnotveryeificaceoua'a distinct yele' lowing takingplace :even' whenappreciable amounts' of alkalies are used. Itis thus seen that while the-present :invention' is: applicable 'to -white'-pigments of themetals of the second and fourth groups of the; periodic table, it. has Y little beneficial efiect' when applied toantimonyeoxide,

-the only commercially importantwhitepigment ,of a metal falling outside these groups-of "the table. While "generally applicable to all other white l pigmented; nitrocellulose "lacquers; the

method has been gfoundtoi be 1 particuarly suited whenused in lacquers containing titanium-di i V.

i I I 5, 2: In "a lacquer comprising nitrocellulose, a V g The 'required-amount ofalkali may be inco r-- e v porated into the lac'quer'in' anyiconvenientman compositions prepared therefromfi While this is Qner, in certain cases it may be more convenient to add it 'directly' tothe finished lacqueresolutionz In the-case of lacquerscontaining ester gum, jthe lime or otherialkali can :be convenient1y incorporated into} the ester solutionito be used;

in the lacquer. This, howevenris not "always eas I V ily done wheredammaris tob'e' usedifsince grinding 5 the dammar. solutionswithsilime sometimes produces certain limeasoaps "which'iare. insoluble in toluol and cause poor compatability inthe jgredientsj of the lacquer.

not the case with all grades ,of dammar, it occurs with many of them and complicates the process to some extent. I Avery distinct advantage of the method for reducingv the tendency for lacquers to yellow which has been .set forth hereinabove' is the fact that the, treatment specified apparently has little, any; harmful effect on either the final. lacquer film or upon the lacquer'solutio'n which retains its improved properties, once it has beentreated. In; order to reduce as far as possible any tendencyftowards' reducing the durability of the fin-al film it isof course preferred to use the minimum'ambunt of alkali which will give the idesiredre'sults. This is readily accomplished the cases where thergum solution may be treated-withgthe alkali. In such cases," the ex-- jcessofalkali, and any precipitate'that may be formed after agitation of the alkaliin the gum solution may be removed before adding the gum solution.- to the remainder oftheiconstituents of thedacqu'en; Where it is found necessaryto increase the amount'of alkali, it is generally ad.- visable to increase somewhat the amount of plasticizerusedinthelacquer. ,The termiwhite pigment!v has. been us'ed in theipresent specification and claims in, the generally accepted sense of'a substantially insoluble, 'finely .divided, .and relatively opaque white substance Y which is,- compatibl e with the other .in-

:Whatis claimed is: .1. In .a lacquercomprising; nitrocellulose, a resin "selected from the group consisting of naturalrresins andester. gum, andv a white pigment. oi-.ametalof the'second and-fourth groups'of 'theperio'dic table, whichilacquer'is normally sube ject to'yellowingwheniexposed in a filmzto sun light, ..the improvement i comprising incorporating in such: a lacquer. a material selected from the counteract'the tendency of said laquer to yelresin selected from the" group consisting of-natgroup consisting of alkali" and alkaline earth oxides ,andhydroxides; in 'sufiicient quantity to uralresinsa'ndestergum, and a white pigment of a-metalbf thesecond-and fourth groups of the periodic table, {which lacquer is normally subiecttoyellowing' when exposed in a film-to sunlight, the; improvement "comprising incorporatingin such a'l'acquer from 0.05% to 1.0% by weight of a material selected from the group consisting of alkali and alkaline earth xides andhydroxides', to'counteract the tendency of aid lacquer to yellow.

7 j CI-IARLES BOGINQJ' 

